The present invention relates to an anti-fouling system for substances in contact with seawater such as ships, offshore structures, undersea structures, bridge beams, rearing crawls, quaywalls, canals, gates, power plants, water intake-drainage pipes, water intake-drainage ducts, etc.
In order to prevent fouling on substances such as ships, offshore structures and the like being in contact with seawater, a method to coat the areas contacting seawater with anti-fouling paint has been generally used.
There are, however, the following drawbacks in this method:
(1) The conventional method can comply with changes in seasons, ocean currents, and water quality with flexibility due to its inability to control the elution speed of anti-fouling ingredients.
(2) As the poison content in the anti-fouling paint is not permitted to exceed a limit, the anti-fouling paint must be recoated every two years.
The applicant has developed equipment to generate effective ingredients to prevent adhesion of marine organisms wherein insulating paints 3 (see FIG. 1) such as epoxy resin and conductive paints 5 in which carbon powder is mixed with organic binder are coated on a structure 1 in contact with seawater 2, and direct current is supplied from a power source box 7 between the conductive paints 5 and an electric conductor 6 composed of steel and the like with the conductive paints 5 as an anode and the electric conductor 6 as a cathode wherein the effective ingredients are generated on the conductive paints 5, which is shown in FIG. 10 and disclosed in Japanese Patent Provisional Publication No. 63-101464 (No. 101464 1988) and No. 63-103789 (No. 103789 1988).
However, it has become clear that this method has the following disadvantages:
(1) Though the electric current density in seawater 2 must be maintained at more than a fixed value, due to a rise in resistance caused by consumption in the conductive paints 5, electric current density tends to be concentrated near a connecting terminal which makes the effective anti-fouling range narrow.
(2) Due to a difference in electric current density caused by irregularity of thickness of the conductive paint 5, it is hard to maintain an expected performance.
(3) Conductive paints of low resistance are required for uniformity of electric current density. To produce paints having such properties, a large quantity of conductive powder must be mixed in which makes the production troublesome.
(4) Because the effective anti-fouling range, a reaching distance of electric current density required for prevention of fouling, is narrow or short, the system is difficult to apply to large-size structures.